US County-Level Variation in Availability and Prevalence of Black Physicians in 1906

Key Points Question Using physician data from the first American Medical Directory (AMD) published in 1906, which county-level characteristics are associated with the availability and prevalence of Black physicians in the South? Findings In this cross-sectional study of 1570 counties, those with lower proportions of Black residents, lower population densities, and greater distances to Black medical schools were more likely to have no Black physicians. Among counties with at least 1 Black physician, higher numbers of Black physicians were associated with lower illiteracy rates among US-born White residents, lower percentage Black population, lower population densities, and shorter median distances to training for Black physicians. Meaning These findings suggest that the dataset created in this study may help elucidate key physician- and county-level patterns associated with early racial inequalities in the US medical profession.

eFigure 1. Extract from a page of the 1906 American Medical Directory. 2small number of institutions were also described as "colored" in the AMD: Louisville National Medical College, Flint Medical College of New Orleans University, Leonard School of Medicine of Shaw University, Knoxville Medical College, University of West Tennessee, and Meharry Medical College.Not all physicians who attended these schools were identified as Black in the AMD; thus, a more expansive Black race variable was created to include all graduates of these institutions (n=113) in addition to those specifically identified in their AMD entry (n=632).Howard University, known in modern times as a prominent HBCU, admitted students of all races, and therefore was not used in this reclassification.4 eTable 1 describes state-level differences in Black physician counts according to these classification approaches.
The questions of where racial labelling originated and how it was implemented are more challenging.The Standard Directory, purchased by the AMA as the foundational Directory dataset, did not include racial designations. 5Biographical cards" requested by AMA and state medical societies (in the South and beyond), and published in the pages of JAMA and state medical journals, did not request racial details. 6 Some county-level societies similarly published blank card forms, hoping that physicians would help update their records; an example of this from Arkansas includes nothing about race.7(p22) Digitized biographical cards -now available as the "Deceased Physicians File"provides further clues but no answers.8 The "(col.)" label appears on many Black physicians' cards, though at least example suggests these labels were added after 1906 and based on information gleaned from state society publications.9,10 Taken together, this seems to suggest a local origin for the labels, which were centrally codified by AMA.Local physicians were likely to be to known to county medical society secretaries, who were charged with collecting and verifying Directory records.11 It is possible that these officialsin the South and beyondadded labels based on their perception of physicians' race.While the question of racial perceptions is one that others have explored in the context of other historical datasets (e.g., Census enumerators), a conclusive answer is beyond the scope of this paper.Still, the expanded racial classification used in this paper (physicians with the label or those who attended Black medical schools) addresses some of the uncertainty surrounding the label.

S1.2. Database validation
A 10% random sample of directory pages (n=25) were selected for auditing by trained research assistants to verify physician records (n=3528) including their location, medical school information, and racial classification status.No errors were found in location or medical school information, and only minor differences were identified in the racial classification (1 "(col.)"identifier occurred in a non-standard place and was not originally identified as Black; another was misclassified as Black due to the string "col."being used as an abbreviation of the word "college").Additionally, all physicians classified as Black in the database were cross-referenced in the original directory document.A further 322 physician records were hand-checked if they reported attending a predominantly Blackserving medical institution, but were not otherwise classified as Black.

S1.3. Exclusions
A small number of physician entries were excluded from analyses: physicians listed as "not in practice" (n=116), and those who attended "fraudulent" medical institutions (n=27).Of these exclusions, Black doctors only comprised 1.5% of those listed as not in practice (n=7).

S1.4. Terrain Ruggedness Index
To represent how some counties may have been physically difficult to access, a modern measure of terrain ruggedness is used. 12While this modern measure could differ from the terrain of the study period, the index primarily captures the mountainous regions of the South (see eFigure 2), rather than small-area differences (e.g., levelling of surfaces for urban development).eFigure 2. Terrain Ruggedness Index S1.5.Sensitivity analyses Census records of employment provide another alternative data source for exploring the distribution and characteristics of physicians by race.Full-count Census records from 1900 and 1910, for instance, can reveal where Black and White physicians resided (aggregated by county). 13Notably, these residence-based records could differ from places of practice.Additionally, these self-reported occupation records could be subject to the same kinds of quality biases for which Polk's Register was criticized.Most critically, these records provide no information on the places or years of medical training, features that enable the AMA Directory dataset to help illustrate issues in the pipeline of medical education.
Despite the shortcomings of the Census occupational records, they offer a useful means of triangulating the patterns observed in the AMA Directory dataset.An analogous inequality measure was constructed using 1910 Census counts of physicians by race.Thus, an indicator of potential under/overcounts of White or Black physicians in the AMA dataset was used to filter data in descriptive statistics and included as a covariate in statistical models to help mitigate the effects of potential discrepancies.To further consider the kinds of places that may be especially subject to discrepancies between the AMA Directory and Census records, multivariate linear regressions were performed to examine how differences in the count of White and Black doctors varied according to county characteristics.
While it is beyond the scope of this paper to discern whether these discrepancies are an artefact of differences in construct (i.e., place of practice versus place of residence) or timing (i.e., 1906 versus 1910), or are true under/overcounts in the AMA Directory, these detectable associations are worth noting for researchers who may use the dataset in their own analyses.Further research, especially archival and historical analyses, may help illuminate more about the racial labelling practices in the AMD, and how these interface with individuals who could "pass" as White. 14

- 18 eTable 1 .
Summary of Black Physician Counts Using Different Racial Categorization Systems